The invention relates to a method for the automatic control of batch processes by means of a process control in which automatic control programs access individual sequential controls.
Batch processes are processes in which the desired product is produced in a time-sequential succession of process-engineering subtasks according to a predetermined specification. The sequence of such processes can be controlled by means of an automatic process control. Such automatic process controls consist of two basic blocks, the hardware and the software.
The hardware components comprise one or more central processor units with internal or external storage units and input and output units, for example analog or binary input and output cards for communication with the systems to be controlled; keyboard, mouse or light pen for operating the process control and display screen or printer for observing the process control.
The software contains the formulation programs and/or general interlocking and/or sequence programs and the process-relevant software components. The formulation programs are the process specifications with the basic operations and their sequential organization for producing a product in the batch process to be controlled. Such formulation programs are usually structured into partial formulations which control the parallel or sequential execution of subtasks in different process units.
The elementary modules of the formulation programs or partial formulations are the phases. The phase programs are structured into the control part (sequential part), the parameter part and the communication part. The control part contains the program elements for the step sequence of the basic operations of the process with the particulars of the initial conditions, the process steps and their combination, the final conditions and the step sequence in the event of malfunctions. The parameter part for controlling a chemical process may comprise, for example, the feedstocks and their amount, the normal time for a process step, the process variables (setpoint values and limiting values for temperature, pressure etc.) and the permissible operating actions. The communication part contains the program components for the data exchange between the phases and the data exchange with the operator for signaling faults or the current state of the process. The communication part further contains the program elements for activating the process-relevant software of the individual control level, that is to say the individual control modules which effect, for example, the activation of the controllers, valves or motors of the process system.
The process-relevant software, that is to say the modules for individual activation, are programs which are activated by the sequence programs (formulation) and convert their commands for controlling one or more operands (actuators), for example controllers, valves, motors.
FIG. 1 shows the principle of the process control of a batch process corresponding to the prior art: The formulation program for controlling the entire process contains a plurality of partial formulations, called automatic control programs here. During the program execution, the automatic control programs directly access the hardware of the plant or activate one or more individual control modules for the activation or interlocking of controllers, valves or motors. In this process, the individual control modules activate, in each case, an actuator in the field. During the sequence of the process control, feedback on the state of the equipment in the field is given to the individual control level or to the automatic control programs and to the process operating/process monitoring system.
During the program execution, different automatic control programs in some circumstances simultaneously access one individual control module or one actuator in the field. The frequency of such simultaneous activations or the interlockings thereof increases drastically with increasing complexity of the software programs. If, in the case of such complex programs, malfunctions are then signaled to the operating personnel, for example "opening of a valve is interlocked", it cannot be unequivocally analyzed where the error originates from. The malfunction may originate from a defective sensor, the error may lie in the hardware of the process control (defective card, blown fuse), it may concern a program error in the sequence chain of the formulation programs, there may be an operating error (valve is set for manual operation) or the interlocking may have been initiated by the process conditions (pressure in the vessel too high, opening of the valve therefore interlocked).
If the software interface of the formulation programs to the hardware is carried out according to the prior art, via an individual control level, as in FIG. 1, although the operating personnel in the control room still have the opportunity to distinguish whether the error lies in the field equipment, it is not possible to give more comprehensive information as to whether the error then lies in the automatic control programs or in the hardware. It cannot be readily ascertained which currently accessing automatic control program is currently performing which function. The causes of, for example, a machine-protection interlocking, a process-dependent interlocking or an activation lock cannot be recognized. Although, using the process control methods known hitherto, it is possible to ascertain the status of an actuator, it cannot be understood how, by means of which accesses of which basic functions of the phases of the process control, this status has occurred.
In "Automatisierungstechnische Praxis--ATP. Vol. 31, No. 6, June 1989, Munich, pages 282-286", a standard software package "basic functions" is described, which is tied to superimposed automatic control programs. For process monitoring, it can be displayed whether a basic function is currently accessing an actuator (LUPE), which interlocking conditions apply to which basic functions (VERA) and which basic functions can be operated by an actuator (GFLI). The storage, actuator by actuator, in an intermediate level of phases of the automatic control programs for the activation (for example from basic functions) and for the interlocking and for the switch-on blocking of one or more actuators and the logical combination thereof is not described and not suggested by anything.
"Automatisierungstechnische Praxis--ATP, Vol. 30, No. 4, 1988, Munich, pages 186-190 describes a standard software package "basic functions" which is integrated into a process control system. For monitoring the process to be controlled, the statistical operating statuses of the actuator and the activation (basic function) currently effective are displayed. The storage of the phases of the automatic control programs which affect the activation, interlocking and switch-on blocking, and also the process-logical combination thereof, in a separate program level is not described. The output to the operating/monitoring system of the currently effective activations, interlockings and switch-on blockings and the process-logical combinations thereof are also not described.
The object was therefore to develop a method for the automatic control of batch processes by means of a process control in which automatic control programs access individual sequential controls, by means of which method the current activations of the individual activations of the actuators in the field are recognizable such that unambiguous information about malfunctions and their causes is possible, which is essential for the elimination of malfunctions and is a decisive factor for the safety, availability and economic efficiency of a plant.